Hi @jensguck,
Thanks for posting! Generally a core starting up and only flashing white indicates that the core is having problems talking to the CC3000 wifi module. I’m still not 100% sure why cores like this pass testing at the factory and then fail on arrival. I’m starting to suspect water damage or severe shipping G’s or other damage.
If you’re interested in troubleshooting, would you be willing to try (if not you can skip this part):
1.) Putting the core in a zip-seal plastic bag of dry rice (like you would if you got your smartphone wet) for 4-8 hours, and try it again?
2.) Make sure you do a factory reset - https://www.youtube.com/watch?v=nGBSYyTo5xA
If neither of these work, or you’d rather not troubleshoot, could you email us at hello@spark.io and we’ll exchange your core for a working replacement. 
Thanks,
David